After re-reading this thread, I realized I forgot to mention some of the most important ways to stay warm especially in small spaces where it really isn’t safe to run any type of combustion heater, and maybe not even a typical electric heater.
Available at many truck stops, and I’m sure online too, you can get 12v plug into the cigarette lighter, heating seat cushions and blankets. Just be sure to get the ones with adjustable temperature settings because they will hold a specific heat level and use much less power.
I actually have the more deluxe version of both of those that both heat and cool. These have tubes of liquid running through them, and I believe they are thermo-electric (Peltier powered). I have these seat cushions in my drivers seat, my cabin seat, and one on top of my bed under the top sheet, folded out flat. Then I have one of the blankets on top of my bed, and one within easy reach of my cabin chair. I never run more than one at a time, but they will keep you either warm or cool regardless of the weather or outside temperatures. They draw 5 amps @ 12v when they’re actually heating or cooling, but that’s only about 1 minute out of every 10. Using one both day and night adds up to about 10 amps per day, not bad at all. Only 3-5 amps if just overnight.
While I don’t have personal experience, they also have heating & cooling clothes available. They might be USB powered or rechargeable. Regardless, if you can’t run a combustion heater, and don’t have shore power available, you can still stay warm or cool while also staying safe.
Also worth mentioning are the Zippo style of hand/pocket warmers. Much cheaper than the disposable ones in the long run.
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